(CNN) -- A piece of ice four times the size of Manhattan island has broken away from an ice shelf in Greenland, according to scientists in the U.S.

The 260 square-kilometer (100 square miles) ice island separated from the Petermann Glacier in northern Greenland early on Thursday, researchers based at the University of Delaware said.

The ice island, which is about half the height of the Empire State Building, is the biggest piece of ice to break away from the Arctic icecap since 1962 and amounts to a quarter of the Petermann 70-kilometer floating ice shelf, according to research leader Andreas Muenchow.

"The freshwater stored in this ice island could keep the Delaware or Hudson rivers flowing for more than two years. It could also keep all U.S. public tap water flowing for 120 days," Muenchow said.

Muenchow's team is studying ice in the Nares Strait separating Greenland from Canada, about 1,000 kilometers south of the North Pole.

Satellite data from NASA's MODIS-Aqua satellite revealed the initial rupture which was confirmed within hours by Trudy Wohlleben of the Canadian Ice Service, according to the University of Delaware website.

Muenchow said the island could block the Nares Strait as it drifts south, or break into smaller islands and continue towards the open waters of the Atlantic.

"In Nares Strait, the ice island will encounter real islands that are all much smaller in size," he said.

"The newly born ice island may become land-fast, block the channel, or it may break into smaller pieces as it is propelled south by the prevailing ocean currents. From there, it will likely follow along the coasts of Baffin Island and Labrador, to reach the Atlantic within the next two years."

Environmentalists say ice melt is being caused by global warming with Arctic temperatures in the 1990s reaching their warmest level of any decade in at least 2,000 years, according to a study published in 2009.

Current trends could see the Arctic Ocean become ice free in summer months within decades, researchers predict.